China is considering plans to build a high-speed railway line to the US, the country's official media reported on Thursday.

The proposed line would begin in north-east China and run up through Siberia, pass through a tunnel underneath the Pacific Ocean then cut through Alaska and Canada to reach the continental US, according to a report in the state-run Beijing Times newspaper.

Crossing the Bering Strait in between Russia and Alaska would require about 200km (125 miles) of undersea tunnel, the paper said, citing Wang Mengshu, a railway expert at the Chinese Academy of Engineering.

"Right now we're already in discussions. Russia has already been thinking about this for many years," Wang said.

The project – nicknamed the "China-Russia-Canada-America" line – would run for 13,000km, about 3,000km further than the Trans-Siberian Railway. The entire trip would take two days, with the train travelling at an average of 350km/h (220mph).

The reported plans leave ample room for skepticism. No other Chinese railway experts have come out in support of the proposed project. Whether the government has consulted Russia, the US or Canada is also unclear. The Bering Strait tunnel alone would require an unprecedented feat of engineering – it would be the world's longest undersea tunnel – four times the length of the Channel Tunnel.